The background art will be described below while mentioning documents.
Undermentioned non-patent document 1 summarizes the trend of domestic and international photonic crystal research, and introduces, relatively in detail, the results of various research facilities (enterprise, university, national research institute, etc.) from the theoretical background to the design technique, specific manufacturing methods, and from materials to the application of devices and the like.
Besides, hitherto, examples in which design and manufacture have been made on a switch, a resonator, and a filter using mode coupling of plural waveguide will be described below.
Undermentioned non-patent document 2 describes a typical branched type interferometer structure (Mach-Zehnder type) optical switch device using a photonic crystal structure. With respect to this, although there are many examples of trial manufacturing in other documents, the operation principle of this device is not a directional coupler type which the invention uses.
Undermentioned non-patent document 3 discloses simulation on an optical switch which is of a directional coupler type using mode coupling between two line defect waveguides formed in a hexagonal lattice photonic crystal and is operated by the applied external electric field. However, there is disclosed only a comparison with a conventional optical switch using a structure other than the photonic crystal, and there is no disclosure on a specific improvement plan and a design guidance concerning the reduction in coupling length of the optical switch using the photonic crystal structure. Besides, the use of nonlinearity by quantum dots or ion doping is not described, and an example of trial manufacturing is not found also in other documents.
Although undermentioned non-patent document 4 discloses that an optical resonator based on a directional coupler type operation principle can be realized, its structure does not use the photonic crystal. Non-patent document 5 discloses simulation on a directional coupler type filter using mode coupling between two line defect waveguides formed in a hexagonal lattice photonic crystal or on a demultiplexer. However, countermeasures for reduction in coupling length are not disclosed.
Further, undermentioned patent documents 1 to 4 disclose optical devices using photonic crystals. For example, patent document 1 discloses an optical switch device of a branched type interferometer structure having a photonic crystal structure as described in non-patent document 2. Besides, patent document 2 discloses an optical modulator device which can output an optical signal faithful to the waveform of an electric signal by a simple structure. Patent document 3 discloses an optical circuit in which three photonic crystals are arranged while crystal orientations are selected so as to obtain a parallel light flux, branching and bending, and the parallel light flux having a high degree of parallelization is obtained in a self waveguide manner. Patent document 4 discloses a photonic crystal optical waveguide as described in non-patent document 3 and a directional coupler device.
Besides, with respect to a method of forming a two-dimensional or three-dimensional defect structure in a photonic crystal, undermentioned patent document 5 discloses a photonic crystal in which a polymer relatively easy to process is used as a material in addition to a semiconductor. Besides, undermentioned patent document 6 discloses a photonic crystal formed of ceramic, and undermentioned patent document 7 discloses a method of filling a hole with another functional material having an amplification effect or the like. Further, as a forming method of a three-dimensional photonic crystal, various forming methods such as an autocloning method and a method for Wood-pile structure are known. In this point, for example, see patent documents 8 and 9, etc.
Patent document 1: JP-A-2002-303836
Patent document 2: JP-A-2002-196296
Patent document 3: JP-A-2002-169048
Patent document 4: JP-A-2001-281480
Patent document 5: JP-A-2003-43273
Patent document 6: JP-A-2001-72414
Patent document 7: JP-A-2002-277659
Patent document 8: JP-A-2001-249235
Patent document 9: JP-T-2001-518707
Non-patent document 1: “Present state of photonic crystal research and future outlook—revised edition—Aiming at technology road map—”, OPTOELECTRONIC INDUSTRY AND TECHNOLOGY DEVELOPMENT ASSOCIATION (Photonic crystal breakthrough technology forum), March 2002 (Heisei 14), 14-013-1
Non-patent document 2: Kazuhito Tajima, “All-optical switch with switch-off time unrestricted by carrier lifetime”, Japanese Journal of Applied Physics, Vol. 32, Part 2, No. 12, 1993, pp. L1746-1749
Non-patent document 3: Hirohito Yamada, “Theoretical analysis of photonic crystal directional coupler type optical switch”, 2002, Electronics Society Conference of the Institute of Electronics, Information and Communication Engineers, C-4-7
Non-patent document 4: Kiyoshi Kishioka, “Characteristics of optical resonator composed of the nonlinear directional coupler”, Transactions of the Institute of Electrical Engineers of Japan, A, vol. 123, No. 12, 2003, p. 1166-1173
Non-patent document 5: J. Zimmermann, M. Kamp, A. Forchel, R. Marz, “Photonic crystal waveguide directional couplers as wavelength selective optical filters”, Optics communications 230, 2004, pp. 387-392